Retinal detachment occurs when the sensory layers of the retina become separated from their underlying supporting tissue of retinal pigment epithelium and the choroid. Generally, retinal detachment is caused by a retinal tear or the presence of vitreous traction, either of which may occur spontaneously or may be due to trauma. Retinal detachment may also result from pathology, such as retinopathy of prematurity in premature infants or diabetic retinopathy in diabetic individuals. Symptoms of retinal detachment are painless and sudden segmental or total visual loss in one eye.
When there is a tear, or when there is traction causing separation of the retina from its underlying structures, the liquid vitreous passes through the opening and into the subretinal space, inducing further exudation in the subretinal space. The retina gradually separates and detaches from the underlying retinal pigment epithelium. This deprives the outer retina of its normal supply of oxygen and nutrients from the choroid. With time, retinal detachment also results in loss of vision, due to loss of photoreceptor cells located in the outer part of the retina.
Treatment of retinal detachment involves reestablishing the connection between the sensory retina and its underlying supporting tissue. If a detached retina is not timely repaired, the retinal pigment epithelium and glial cells proliferate, forming fibrous bands under and in front of the retina which hold the retina in a fixed and detached position. Therefore, in primary or chronic retinal detachment, a goal of treatment is to reattach the retina as quickly as possible after detachment occurs.
Treatment methods to reattach a detached retina include scleral buckling, pneumatic retinopexy, and vitrectomy with the use of a tamponading agent. None of these methods is entirely satisfactory.
Retinal reattachment by scleral buckling involves an invasive surgical procedure using local or general anesthesia. The conjunctiva is separated from the sclera, the retinal tear is localized, and subretinal fluid is drained by cutting through the sclera and choroid. The retinal tear is coagulated using, for example, an argon laser. An implant, such as a sponge or piece of silicone, is then sutured over the sclera, pushing the eye wall inward and supporting the retinal tear from the outside. The patient requires about ten days to recover. Disadvantages are that the patient must undergo a surgical procedure and endure a long recovery period, and must tolerate the presence of a buckle around the eye that might interfere with movement of the eye.
Retinal reattachment by pneumatic retinopexy does not involve opening the conjunctiva, but instead involves injecting an expanding biocompatible gas into the vitreous cavity. About 0.3-0.5 ml of such a gas is injected into the vitreous cavity, where the gas expands from about three to about six times its volume. The patient is instructed to maintain a strict head position, allowing the expanded gas bubble to tamponade the retinal tear. However, the force of injection itself can force the subretinal fluid through the tear into the vitreous cavity. Cryocoagulation may be applied to the retinal tear to create scar tissue, closing the retinal tear. Alternatively, the subretinal fluid may resorb by itself within about 24 hours, after which laser coagulation can be performed.
There are several disadvantages of pneumatic retinopexy. Only superior tears can be treated, because air and gas rise above the vitreous fluid, and multiple tears that are separate from each other are difficult to tamponade. Subretinal fluid that is forced into the vitreous cavity may allow proliferation of retinal pigment epithelium cells, which can form membranes and create proliferative vitreoretinopathy (PVR). PVR may further detach the retina and is a serious complication of pneumatic retinopexy. Injection of gas without drainage of fluid may cause a rapid rise in intraocular pressure, thus the patient must be monitored postoperatively for several hours. If needed, the anterior chamber of the eye may be taped and systemic medication may be administered to lower the intraocular pressure. Possible side effects, however, are closure of the central retinal artery which could result in diminished blood flow to the retina. Additionally, in older individuals, the strict head positioning required to effect treatment may be very difficult to achieve and maintain. Still further, the results are unpredictable and a 24 hour waiting period is required to determine if the subretinal fluid has resorbed.
Retinal reattachment using vitrectomy with a tamponading agent is a surgical procedure, requiring local or general anesthesia. Three instruments are placed inside the eye: one is used for infusing fluid, one is used for cutting and removing tissue, and one is used for illumination. The vitreous gel is cut using a vitrectomy instrument and is removed, the intraocular fluid is simultaneously removed with the subretinal fluid, and the intraocular fluid is simultaneously replaced with air or another gas. The retinal tear is coagulated using a laser, with the gas remaining inside the eye for a continuous tamponading effect. Scleral buckling may also be performed to achieve enhanced outcome; this has the attendant drawbacks that have previously been described.
Disadvantages of vitrectomy are that the patient must undergo a surgical procedure with the possibility of injury to the lens or retina during surgery, and has a 70% chance of postoperative cataract formation due to the vitrectomy and the injection of gas into the eye.
Improvements in methods of treating retinal detachment are therefore desirable.